Field sprayers and spray booms hitched to work machines, such as tractors, in some cases have very large working widths of more than 20 meters. Such wide spray booms are folded and collapsed in for transport purposes. In the field, symmetrical cantilevered arms of several meters length are located on both sides of the work machine, which cantilevered arms have a varying spacing from the ground according to surface conditions and field relief. Since the downward-directed nozzles for spreading a spraying agent, for instance, a plant protection agent, which nozzles are arranged on the cantilevered arms, each have a defined spray cone, varying the spacing of the nozzles to the ground results in an uneven covering of the field with spraying agent. In addition, the danger of the spraying agent drifting greatly increases as the distance of the spray nozzles from the ground increases, since even slight air movements negatively affect the finely dispersed drops.
With increasing cantilever dimensions and the associated working width there is therefore a necessity to guide the spray boom at as uniform a spacing from the ground as possible, because minimal inclines of the spray boom will lead to large spacing differences of the nozzles to the ground.
In this context, it is known to suspend a spray boom from a carrier vehicle to be rotatable or pivotable about at least one axis of rotation about a central pivot point. The rotation or pivot axis in this instance preferably runs parallel to the longitudinal axis of the carrier vehicle. In order to ensure an even spreading of the spraying agent, the spacing between the top surface of the growth and the spray nozzles must be constantly controlled to a defined spacing. On horizontal agricultural fields, this can generally be achieved by self-leveling, in which the spray boom aligns itself in the horizontal plane with the center of gravity of the spray boom being located below the pivot point and the spray boom being suspended, for instance, to be freely and swingingly rotatable. The desired effect will not occur, however, for agricultural fields running along a slope.
In order to constantly control to a defined spacing, the spacing between the top surface of the growth for agricultural fields running in any plane and the spray nozzles arranged on a spray boom pivotably suspended about a central pivot point, it is therefore known to pivot the spray boom, which is, for instance, raised to a desired spacing from the ground, about a pivot axis running through a central pivot point such that the spacing is optimized over the entire working width. For this purpose, an alignment changing torque has to be exerted on the spray boom about a pivot axis running through a central pivot point. This is carried out by means of at least one actuator, which transmits, at least as required, a force or a force couple effecting an alignment changing torque about a pivot axis from the carrier vehicle onto the spray boom in order to change the alignment of the spray boom.
This alignment changing torque accelerates the spray boom in a desired target rotational direction. Without countermeasures, the spray boom would continue to rotate about the pivot axis even after the impact of the alignment changing torque has ended, since the spray boom would retain its angular momentum due to the mass moment of inertia. In order to decelerate the spray boom, a braking torque in opposite to the previous alignment changing torque therefore has to be induced. This braking torque counteracts the rotary movement initiated by the alignment changing torque and thus damps the system of the spray boom rotatably suspended about the central pivot point.
Up to now, mechanical dampers, which are arranged between the carrier vehicle and the spray boom, are usually used for generating the braking torque. Assuming that a relative movement in the form of a rotation about the pivot axis occurs between the carrier vehicle and boom, then a mechanical damper mounted in between would counteract the relative rotation or the rotary movement, respectively, of the boom and would decelerate it as desired. If the carrier vehicle, however, rotates about the pivot axis due to bumps, for example, and the spray boom stands still, this will also result in a relative rotation between the carrier vehicle and the spray boom. A mechanical damper arranged between the carrier vehicle and the spray boom would counteract this relative rotation and thus transmit a torque acting about the pivot axis to the spray boom, such that a coupling exists between carrier vehicle and spray boom.
The coupling likewise exists if a measuring system is used as a basis for regulating the torque, which measuring system measures a relative angle and/or a relative rotation between carrier vehicle and spray boom.
In addition, measuring systems are known, which use tilt sensors arranged at the spray boom for determining the position of the spray boom. The angular velocity of the spray boom can be acquired independently of the carrier vehicle from the temporal derivation of the tilt. In the instance of lateral accelerations such as occur, for example, when driving along curves, tilt sensors however provide an incorrect tilt. An incorrect angular velocity will therefore also be calculated.
A spreading device for spreading liquid active agents is known from US 2011/0282554 A1. The device comprises:                a carrier vehicle;        a spray boom arranged on the carrier vehicle, the spray boom comprising a middle part, which is variably adjustable in its spacing from the ground, as well as two cantilevers projecting laterally from the carrier vehicle, which cantilevers are arranged on the middle part to be movable independently of each other about a respective pivot axes running parallel to a longitudinal axis of the carrier vehicle;        distance sensors arranged on the two cantilevers for the purpose of detecting the positions or distances of the cantilevered ends to the ground;        at least one distance sensor arranged on the middle part between the cantilevers for the purpose of detecting the distance of the middle part to the ground;        a control unit processing the output signals of the sensors to control signals;        one actuator respectively acting on one of the two cantilevers, the actuator being in the form of a hydraulic cylinder and having the purpose of individually lifting and lowering each cantilevered end in dependence on control signals from the control unit; as well as        an angle of rotation sensor or an angular rate sensor, which detects the roll angle or the roll rate of the carrier vehicle about its longitudinal axis and which is arranged on the carrier vehicle independently of the spray boom.        
The distance sensors can be LIDAR (Light Detection and Ranging), RADAR (RAdio Detection and Ranging), or ultrasonic sensors, or they can be sensors based on interferometry or on radio frequency, such as, for example, GPS sensors. The angle of rotation sensor or the yaw rate sensor can be a gyroscope. In order to maintain the cantilevered ends at the uniform distance to the ground like the middle part, a vertical error of the two cantilevered ends is first calculated by way of a comparison of the output signals of the distance sensors. If this vertical error is not equal to zero for one or for both cantilevered ends, an initial control signal is generated in order to actuate an actuator assigned to a cantilever in question and to reset the cantilevered end having a vertical error to the specified spacing from the ground. If one of the cantilevers is lifted in the process, this leads to a rolling movement of the carrier vehicle in the direction toward the cantilever to be lifted, whereby, without further measures, the remaining cantilever would have a vertical error resulting from a lowering. In order for a control loop comprised of distance sensors, control unit, and actuators, to be regulation-technically stable and to not build up uncontrollable sway, for instance, and/or to not lead to a lateral toppling of the carrier vehicle, it is provided by means of the control unit to generate a compensation control signal counteracting an instability of the control loop by way of the output signal of the angle of rotation sensor or the yaw rate sensor, which detects the roll angle or the roll rate of the carrier vehicle about its longitudinal axis, and to output to the actuators a control signal determined by way of the initial control signal and the compensation control signal.
A spreading device for spreading liquid active agents is also known from WO 2012/146255 A1. The device comprises:                a carrier vehicle;        a spray boom with cantilevers projecting on both sides of the carrier vehicle, which spray boom is arranged on the carrier vehicle movably about a pivot axis running parallel to a longitudinal axis of the carrier vehicle;        one or more sensors arranged on the spray boom for the purpose of detecting the distances of the cantilevers to the ground, such as one or more acceleration sensors, gyroscopes, and/or distance sensors;        a control unit processing the output signals of the one or more sensors to control signals;        a stabilizing device, which damps vibrations of the spray boom, the stabilizing device comprising two guidings running along the two cantilevers as well as one block arranged to be shiftable along each of the guides; and        an actuating device, which acts on the positions of the two blocks along the guides in dependence on control signals from the control unit.        
As a reaction to undesirable vertical movements, which, in an undampened control loop, can induce rotary oscillations of the spray boom about the longitudinal axis of the carrier vehicle, a damping and compensation by a mass displacement by way of a shift of the blocks along the two cantilevers is provided. Output signals from acceleration sensors, which are fastened at the cantilevers and which detect vertical oscillations of the spray boom, serve as input variable from the control unit, which input variable enters into the control signals to the actuating device. A regulation of the uniform distance of the cantilevers to the ground is not disclosed.
A spreading device for spreading liquid active agents is known from DE 10 2007 045 846 A1. The device comprises:                a carrier vehicle;        a spray boom mounted on a height adjustable parallelogram linkage on the carrier vehicle, which spray boom is movable about a rotation axis running parallel to a longitudinal axis of the carrier vehicle;        an acceleration sensor arranged on the spray boom;        an acceleration sensor arranged on the parallelogram linkage; as well as        a first reference sensor in the form of an acceleration sensor, which is arranged at the carrier vehicle; and        a second reference sensor in the form of a gyrostat or a yaw rate sensor, which is arranged in the area of the frame of the carrier vehicle;        a control unit processing the output signals of the one or more sensors to control signals;        an actuator in the form of a hydraulic cylinder, which acts on the angular position of the spray boom in dependence on control signals from the control unit; as well as        an actuator in the form of a hydraulic cylinder, which acts on the distance of the parallelogram linkage from the ground in dependence on control signals from the control unit.        
Once position and alignment of the spray boom have been manually set, the control signals generated by the control unit prevent position changes when braking or accelerating, during bounding or rebounding, respectively, of the carrier vehicle, or also when driving over bumps. Errors creeping in by way of the different positioning of the acceleration sensors and the reference sensors can be compensated more precisely by the reference sensors. Regulation of the uniform spacing of the spray boom to the ground is not disclosed.
For the sake of completeness, it should be mentioned that, in addition, spray booms are known that consist of segments, which are adjustable relative to one another, in order to allow for a sectional adaptation to the ground contour in the instance of very wide working widths. A spray boom which has a cantilever that is put together of segments is already known from DE 32 02 569 A1. In this instance, individual segments are connected to each other, with the movement of the individual segments in relation to each other being carried out passively. For this mechanism, a supporting element is necessary on the outer side of each of the cantilevers in order to enable the pivoting process.